This invention relates to a method of manufacturing a cathode ray tube comprising a display screen and an electron gun including a cathode, a number of electrodes and a resistive-layer lens system.
A cathode ray tube comprising an electron gun including a cathode, a number of electrodes and a resistive-layer lens system is described in, inter alia, European Patent Application 327149, which corresponds to U.S. Pat. No. 4,945,283 (Jul. 31, 1990).
A resistive-layer lens system contains at least one resistive-layer lens. A resistive-layer lens is an electron-optical element in the electron gun, which element comprises a resistive layer, an electron-optical lens for an electron beam being formed, in operation, by applying a voltage or voltages across the resistive layer. The element may comprise a tubular portion. Said tubular portion is provided with a resistive layer or resistive layers, for example, on the inside, across which resistive layer or resistive layers a potential difference or potential differences can be applied. The resistive layer may be spiral-shaped.
An electron gun comprising a resistive-layer lens system is suitable, for example, for use in a colour cathode ray tube or monochrome cathode ray tube, for example, a projection ray tube.
The shape of the spot, i.e. the target spot on the display screen, of an electron beam generated by the electron gun can be forecast within certain limits by means of electron-optical calculations.
It has been found, however, that during operation of a cathode ray tube having such an electron gun, the spot of an electron beam generated by the electron gun is frequently of an inferior quality to that which was expected on the basis of the electron-optical calculations.